|Property/Characteristic||PVD Coating||TD Coating|
|Coating Temperature (South Africa)||450°C or 520°C||Generally 850 – 1020°C (austenitising temperature of steel)|
|Chemical Composition||TiN, TiAlN, AlCrN, etc||Mainly VC, other compounds possible|
|Micro Hardness||TiN 2300 Hv, TiAlN 3300 Hv, AlCrN 3300 Hv||3200-3800 Hv|
|Adhesive nature to work materials||Low to Very Low||Very Low|
|Thickness||2-4 µm||4 – 6 µm (high impact), 8- 10 µm (form tools)|
|Adhesion to base material||Good, dependent on cleanliness and etch||Best, diffusion bonded|
|Base Material||Best on HSS, 8% CW steels and carbide.||Best on cold work steels and high Co carbide|
|Distortion/size change||Very low to none||Medium to low|
|Sensitivity to cleanliness||Very sensitive to surface condition, oxides and other contaminants.||Low sensitivity to oil, rust, paint etc.|
|Resistance to heat||TiN ~ 600°C , TiAlN ~ 900°C||500°C (oxidizing environement)|
|Prior Nitiriding||White layer can affect adhesion negatively but also provides better support for PVD layer||VN and VCN may formed and this has poor tirbilogical properties.|
|Coating restrictions||Masked from coating where jigging materials are present. Shadowing can occur. Cannot coat some geometries such as deep holes.||Coating develops on all surfaces apart from direct contact areas with jigging areas. Masking not practical.|
|Coatable Size||Ø 135 x 400 mm. Inquire about other sizes||Coatable volume typically 450 x 600.|
|Very thin, long items||No problem||Higher distortion risk|
|Cutting Edges||Good an all edges||Best on cutting edges of > 45° and greater. Acute angles can be a problem.|
|Stripping||Chemical striping, non-aggressive, blasting for low tolerance parts.||Electro-chemical stripping or abrasive blast|
|Costing||Typically based on volume consumed||Typically based on weight|
*For any properties not covered above relating to your application , please consult your TD coating specialist.
Which Coating is better?
Since there are distinct characteristics that separate the two technologies, there are applications where one coating technology has an absolute advantage over its competitor.
Example 1: A flat ejector 2mm thick x 150 mm long , made of HSS would be excluded from TD due to high distortion risk and non-optimum base material suitability. This application would clearly be the domain of PVD, or other technologies.
Example 2: A tube swaging tool with ID 40 x 150, which reduces the OD of a tube through a forming operation. Tool is made of 1.2379, vacuum hardened and tempered at 200 °C. Shadowing of PVD (line-of- site coating) will limit the coating internally through PVD and secondly if process temp is above the 200 °C adhesion and dimension can be jeopardized. TD would form evenly inside the tool ID and OD and be tempered at 200 °C after coating to maintain hardness and dimension with no concern for decreased adhesion.
There are however overlap applications where either of the coating technologies would add benefit and a choice between the two would need to be made. This would naturally put the two coating technologies in competition, however choosing the best coating for the particular application usually boils down to two main criteria.
Bond strength and thickness
Due to the diffusion process, the TD coating has much higher bond strength than that of PVD and is therefore more suitable for very high surface load applications such as pressing of stainless steel and very thick gauge sheet and deep draws. Conversely for low load applications, where more coating translates to longer wear life, TD has an advantage.
Precision however is the forte of PVD coating and due to its lower temperature application, it is the best when tight tolerances are critical, and need to be maintained once the steels have been heat treated correctly.
If neither of these are primary concerns then experience in the particular application, or a trial may be necessary to determine the best value to the customer.
Cost always tends to play a role, but only if the life extension is limited. The longer a coating extends a tools useful life, the greater the leverage effect of the coating.